*{
    margin: 0;
    padding: 0; 
}

.preview_img{
    position: relative;
    left: 500px;
    width: 400px;
    height: 400px;
    border: 1px solid black;
    
}

.mask{
    display: none;
    position: absolute;
    left: 0;
    top: 0;
    width: 200px;
    height: 200px;
    background-color: rgb(154, 92, 255);
    opacity: 0.5;
    cursor: move;
}

.big_box{
    display: none;
    position: absolute;
    left: 410px;
    top: 0;
    width: 500px;
    height: 500px;
    z-index: 999;
    background-color: pink;
    border:1px solid black;
    overflow: hidden;
}

.preview_img .big_img{
    position: absolute;
    left: 0;
    top: 0;
   
}